Ok this post is for me to prove that this game, Alien Hallway, is not bugged with a game braking bug.

In my vid you see I clearly am passed Lvl 4 in my campaign but you see me go back to the lvl and select it and hit the play button. Then ya clearly see me play the level 100% fine and successfully 100% destroy the enemies base and complete the level with 5 stars AGAIN!

So any1 on steam again that wishes to try and say that Lvl 4 in Alien Hallway is impossible to complete can suck it. You obviously have not verified your game or defragged it yet as I do believe that is the solution for your problem if the lvl is bugging out on you. I usually verify my game(s) files then defraggem right after installation.

279 files failed to validate. There was no need for a defrag. And yes it did solve the problem. Although the problem is Steam itself of course, I played through it fine the first time when I bought the game, and my hard disk is in perfect health with no corruptions (I have many important files with parity information and all require no repair).